We learn about characters by what they say, do, think and feel, and how they react to their environments; we also learn about them by what the author tells us about them directly. Since "Araby" is written in first-person, our understanding of the narrator comes from his own words. We learn his thoughts and feelings--about his life and about his romantic aspirations. We know him to be a boy who finds his environment to be devoid of beauty, romance, or adventure and one who longs for those in his life. Making his trip to Araby, and his profound disappointment with what he finds there, reveals much about him.
The other characters are revealed by what the boy tells us about them and by what we can infer from his narrative. We have some insight into the loneliness of the dead priest as he lived and died in the back room, and we gain some understanding of Mangan's sister, a young woman who would "love to go" to Araby, but chooses instead a religious retreat. The narrator's aunt and uncle are revealed through their actions, with his aunt showing more sensitivity to his feelings. The shopkeepers at the bazaar are characterized primarily through their conversation, the dialog that the narrator overhears and repeats in the story.